1. Field of the Invention
This invention relates to a hydrosilation process involving the reaction of a compound containing silicon-bonded hydrogen with a compound containing aliphatic unsaturation in the presence of actinic radiation. The invention further relates to polysiloxane compositions, prepared by said process, which compositions are useful for preparing dental impressions, adhesives, release liners, gaskets, caulking materials, and coatings.
2. Discussion of the Art
Numerous patents teach the use of various complexes of cobalt, rhodium, nickel, palladium, or platinum as catalysts for accelerating the thermally-activated addition reaction (hydrosilation) between a compound containing silicon-bonded hydrogen and a compound containing aliphatic unsaturation. For example, U.S. Pat. No. 4,288,345 (Ashby et al) discloses as a catalyst for hydrosilation reactions a platinum-siloxane complex. U.S. Pat. No. 3,470,225 (Knorre et al) discloses production of organic silicon compounds by addition of a compound containing silicon-bonded hydrogen to organic compounds containing at least one non-aromatic double or triple carbon-to-carbon bond using a platinum compound of the empirical formula PtX.sub.2 (RCOCR'COR").sub.2 wherein X is halogen, R is alkyl, R' is hydrogen or alkyl, and R" is alkyl or alkoxy. The catalysts disclosed in the foregoing patents are characterized by their high catalytic activity. Other platinum complexes for accelerating the aforementioned thermally-activated addition reaction include a platinacyclobutane complex having the formula (PtCl.sub.2 --C.sub.3 H.sub.6).sub.2 (U.S. Pat. No. 3,159,662, Ashby); a complex of a platinous salt and an olefin (U.S. Pat. No. 3,178,464, Pierpoint); a platinum-containing complex prepared by reacting chloroplatinic acid with an alcohol, ether, aldehyde, or mixtures thereof (U.S. Pat. No. 3,220,972, Lamoreaux); a platinum compound selected from trimethylplatinum iodide and hexamethyldiplatinum (U.S. Pat. No. 3,313,773, Lamoreaux); a hydrocarbyl or halohydrocarbyl nitrile-platinum (II) halide complex (U.S. Pat. No. 3,410,886, Joy); a hexamethyl-dipyridinediplatinum iodide (U.S. Pat. No. 3,567,755, Seyfried et al); a platinum curing catalyst obtained from the reaction of chloroplatinic acid and a ketone having up to fifteen carbon atoms (U.S. Pat. No. 3,814,731, Nitzsche et al); a platinum compound having the general formula (R')PtX.sub.2 where R' is a cyclic hydrocarbon radical or substituted cyclic hydrocarbon radical having two aliphatic carbon-carbon double bonds, and X is a halogen or alkyl radical (U.S. Pat. No. 4,276,252, Kreis et al); platinum alkyne complexes (U.S. Pat. No. 4,603,215, Chandra et al.); platinum alkenylcyclohexene complexes (U.S. Pat. No. 4,699,813, Cavezzan); and a colloidal hydrosilation catalyst provided by the reaction between a silicon hydride or a siloxane hydride and a platinum (0) or platinum (II) complex (U.S. Pat. No. 4,705,765, Lewis). Although these platinum complexes and many others are useful as catalysts in processes for accelerating the thermally-activated addition reaction between compounds containing silicon-bonded hydrogen and compounds containing aliphatic unsaturation, processes for promoting the radiation activated addition reaction between these compounds are rare. Platinum complexes that can be used to initiate ultraviolet radiation activated hydrosilation reactions have been disclosed, e.g., platinum azo complexes (U.S. Pat. No. 4,670,531, Eckberg); (.eta..sup.4 -1,5-cyclooctadiene)diarylplatinum complexes (U.S. Pat. No. 4,530,879, Drahnak); and (.eta..sup.5 -cyclopentadienyl)trialkylplatinum complexes (U.S. Pat. No. 4,510,094, Drahnak). Other compositions that are curable by ultraviolet radiation include those described in U.S. Pat. Nos. 4,640,939 and 4,712,092 and in European Patent Application 0238033. However, these patents do not indicate that the platinum complexes disclosed therein would be useful for initiating a visible radiation activated hydrosilation reaction.
Assignee's copending application, U.S. Ser. No. 242,478, filed Sep. 9, 1988, describes a visible radiation activated hydrosilation system. While this catalyst system provides an alternative to UV initiated hydrosilation, several limitations can be cited. First, the system requires both a visible light absorbing sensitizer and a stable UV absorbing photohydrosilation catalyst, for example, an (.eta..sup.5 -cyclopentadienyl)trialkyl platinum complex. Second, relatively high concentrations of the platinum catalyst, up to 1000 ppm platinum, are essential for rapid cure in certain systems. Third, these systems have limited depth of cure. Finally, these systems have only a moderately long shelf-life at room temperature.